Integrated Service (IntServ) versus Differentiated Service (Diffserv)

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Integrated Service (IntServ) versusDifferentiate
d Service (Diffserv)
Information taken from Kurose and Ross textbook
Computer Networking A Top-Down Approach
Featuring the Internet
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Integrated Service (IntServ)

• IntServ framework was developed within IETF to
  provide individualized QoS guarantees to
  individual sessions.
• provides services on a per flow basis where a
  flow is a packet stream with common source
  address, destination address and port number.
• IntServ routers must maintain per flow state
  information.

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IntServ

• two key IntServ features
• Reserved Resources
• the router must know the amount of its resources
  currently reserved for on-going sessions.
• standard resources link capacity, router buffers
• Call Setup
• A flow requiring QoS guarantees must be able to
  reserve sufficient resources at each router on
  path to ensure QoS requirements are met.

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Call Setup details

• Call Setup also referred to call admission
  requires participation of each router on the
  path.
• steps in call setup process
• Traffic characterization and specification of QoS
• Rspec (R for reserved) defines the specific QoS
  being requested by a connection.
• Tspec (T for traffic)characterizes the traffic
  the sender will be sending into the network or
  the traffic that the receiver will be receiving
  from the network.

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Call Setup details

• Signaling for call setup
• A sessions Tspec and Rspec must be carried to
  the
• routers where resources will be reserved.
• RSVP is the signaling protocol of choice.
• Per-element call admission
• Once a router receives Rspec and Tspec for a
  session, it decides whether or not to admit the
  call.

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IntServ traffic classes

• Best Effort service
• Controlled Load service
• A flow receives a quality of service closely
  approximating QoS that flow would receive from an
  unloaded network element.
• This is fine when the network is lightly loaded,
  but the service degrades quickly as network load
  increases.

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Intserv traffic classes

• 3. Guaranteed Service RFC2212
• Provides firm bounds on queueing delays that a
  packet will experience at a router.
• A sources traffic characterization is given by a
  leaky bucket with parameters (r,b) and requested
  service is characterized by transmission rate, R.
  This characterization is requiring a forwarding
  rate R at each router and a bound on maximum
  queuing via the leaky bucket parameters.

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Differential Service (DiffServ)

• In DiffServ, flows are aggregated into classes
  that receive treatment by class.
• More complex operations are pushed out to edge
  routers and simpler operations done by core
  routers.
• motivated by
• scalability, flexibility, and better-than-best-eff
  ort service without RSVP signaling.

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DiffServ functional elements

• edge functions
• packet classification
• packet marking
• traffic conditioning
• core functions
• forwarding based on per-hop behavior (PHB)
  associated with packets class

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DiffServ edge functions

• packet classification
• classifier selects packets based on values in
  packet header fields and steers packet to
  appropriate marking function
• how classifier obtains the rules for
  classification not yet addressed RFC 2475 uses
  term behavior aggregate rather than class of
  traffic.
• administrator could load table of source
  addresses
• done under control of TBA signaling protocol

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Meter
Shaper/ Dropper
Forward
Classifier
Marker
Packets
Drop
Logical view of packet classification and traffic
conditioning at the edge router
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DiffServ edge functions

• packet marking
• DS field value set accordingly at the marker.
• may wish to limit injection rate of specifically
  marked packets into network, i.e., user promises
  to keep sending rate within a traffic profile.
• metering function compares the incoming packet
  flow with negotiated traffic profile.
• This implies a traffic shaper/dropper function.

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DiffServ core routers

• Routers define packet classes and separate
  incoming packets into classes.
• Treatment is done per class.
• Per-hop behavior (PHB) defines differences in
  performance among classes.
• externally observable performance criteria that
  do not specify internal implementation mechanisms
  at router.

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per-hop behavior (PHB)

• examples
• A given class receives at least 10 of outgoing
  link bandwidth over time interval.
• Class A packets have strict priority over class B
  packets.
• current proposals for PHB
• Expedited Forwarding (EF) PHB
• Assured Forwarding (AF) PHB

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Expedited Forwarding (EF) PHB

• EF specifies that the departure rate of class of
  traffic from router must equal or exceed a
  configured rate independently of the traffic
  intensity of any other classes.
• This implies some form of isolation among traffic
  classes.
• EF abstraction a link with a minimum
  guaranteed link capacity

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Assured Forwarding (AF) PHB

• Assured Forwarding divides traffic into four
  classes where each AF class is guaranteed some
  minimum resources (capacity, buffering).
• Within each class, packets are further
  partitioned into one of three drop preference
  categories. Congested routers then drop/mark
  based on their preference values.

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Assured Forwarding (AF) PHB

• Determining resource allocation per class of
  service must be done with knowledge about traffic
  demands for the various traffic classes.